A model for the generation of multiple A to G transitions in the human respiratory syncytial virus genome: predicted RNA secondary structures as substrates for adenosine deaminases that act on RNA.

Human respiratory syncytial virus (HRSV) escape mutants selected with antibodies specific for the attachment (G) protein contain diverse genetic alterations, including point mutations, premature stop codons, frame shift changes and A to G hypermutations. The latter changes have only been found in mutants selected with antibodies directed against the conserved central region of the G protein. This gene segment fulfils substrate requirements for adenosine deaminases that act on RNA (ADARs): i.e. it is an A+U rich region of 137 residues, and 98 or 106 of them--for A/Mon/3/88 or Long HRSV strains, respectively--are predicted to form intramolecular base pairs leading to a stable RNA secondary structure. In addition, when sequences of the G gene from natural isolates are compared in terms of pairwise substitutions, A to G+G to A changes are preferentially observed in regions where stable intramolecular dsRNA secondary structures are predicted to occur. In this study, a model is proposed in which, in addition to nucleotide misincorporations, reiterative A to G changes in HRSV are generated by ADAR activity operating in short segments (100-200 ribonucleotide residues) of the HRSV genome with high tendency for intramolecular base pairing.